JPH0676111A - Character reading method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a character reading method capable of reliably reading characters printed on objects having various shapes such as steel materials regardless of lighting conditions. [Structure] Characters printed on the surface of a plurality of types of objects are respectively photographed, and the images are displayed with a preset threshold value.
In the character reading method that digitizes the character part by extracting the value and further identifies the character, the illuminance distribution in each area of the surface of the object when illuminated is measured for each type of object, and the A threshold value is set for each object and each area from the measurement results, and the captured image of each area of each object is binarized with the threshold value corresponding to that area, so that the printing surface is not uniformly illuminated. However, since the binarization threshold value is optimized for each area of each object, proper binarization can be performed, and the correlation rate of the extracted character pattern with respect to the reference pattern is maintained at a high state. Readability is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a character reading method,
In particular, the present invention relates to a character reading method suitable for reading characters printed on an object such as an end surface of a steel material by a paint spraying type printing device under bad reading conditions such as environmental temperature and lighting.

[0002]

2. Description of the Related Art Conventionally, a character string printed on the surface of an object is photographed by a camera, the image is binarized with a preset threshold value, and the character string portion is extracted as a pattern. There is a character reading device that compares each character with a reference pattern to identify and identify each character, and reads the content of the character string.

On the other hand, at the entrance of the heating furnace for heating the steel material, the operator sprays paint on the end surface of the steel material as to whether or not the transported steel material is the steel material to be heated. It was judged from the character string such as the serial number printed by the device. It is conceivable to use a character reading device to judge this character string. Normally, in the character reading device as described above, the objects to be read have the same size and shape, and the illumination is uniform over the entire printing surface. It is intended for those who have. However, for example, when reading the one printed on the end surface of the steel material, the relationship between the width and height of the steel material and the illuminance distribution on the surface of the steel material is shown in FIG. As indicated by the symbol A), the illuminance is not constant between the central portion and the edge portion of the printing surface, so that it is difficult to set the binarization threshold value and it is difficult to read characters.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2-188891, the photographed image is divided into a plurality of regions,
It is conceivable to set a different threshold for each area.

However, particularly in the case of objects having various shapes such as steel materials, the distance to the illumination of the printing portion is different for each shape, and therefore, as shown in FIGS. 3B and 3C, a pattern different from A is used. Therefore, it is difficult to perform proper binarization simply by setting another threshold value for each area.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a character reading method capable of reliably reading characters printed on objects having various shapes such as steel regardless of the state of illumination. It is intended to be provided.

[0007]

According to the present invention, the above-mentioned objects are photographed by illuminating characters printed on the surface of a plurality of types of objects having different shapes with a lighting device and photographing the characters. In a character reading method in which an image is binarized, a character portion is extracted as a pattern, and the character is specified by comparing with a reference pattern, the illuminance in each area of the object surface when illuminated by the illumination device. A distribution is measured for each type of the object, and a binarization threshold value is set for each of the areas of each of the objects based on the measurement result, and a captured image of each area of each of the objects is set to the area. It is achieved by providing a character reading method characterized by binarizing with a threshold value corresponding to.

[0008]

In this way, the illuminance distribution on the printed surface is measured for each object, and 2 is calculated for each area of each object based on this illuminance distribution.
By setting the binarization threshold value, binarization is optimized for each object and each region.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of the character reading device.
The industrial camera 1 is arranged at a position facing the end faces 2a of the plurality of steel materials 2 transported by the transportation device 7.
Each steel material 2 in the present embodiment is composed of three kinds of steel materials having different heights and widths from each other, and these steel materials 2 are arbitrarily set, for example, as a set of three, and are conveyed by a rail and a drive mechanism. It is designed to be conveyed by the device 7. The industrial camera 1 is traversed by three traversers 3, 4, so that it can be moved in three axial directions of X axis (left and right), Y axis (front and back), and Z axis (up and down).
It is supported by 5. A lighting device 6 is provided between the industrial camera 1 and the steel material 2. A position sensor 8 for detecting the side edge of the steel material 2 of each set is provided near the lighting device 6 so as to stop each set of the steel material 2 in front of the industrial camera 1 and the lighting device 6. . Also, steel material 2
A steel material end face positioning mechanism 9 is provided at the front position in the conveying direction for each set of steel products 2 to keep the distance of each end face 2a to the industrial camera 1 and the illumination device 6 constant.

On the end surface 2a of the steel material 2, a character string 10 consisting of 7 matrix characters each having 5 dots horizontally and 7 dots vertically is previously printed by a paint spraying type printing device. The character string 10 has substantially the same number of characters, character spacing, character shape, character printing direction, and character size, but the printing position differs depending on the shape of the steel material 2.

On the other hand, the camera 1 is connected to an image processing device 11 for analyzing the image signal, and binarizes a video signal based on an algorithm described later to perform a character reading process. The image processing apparatus 11 is connected to the computer 13. The computer 13 instructs the traverser controller 14 which drives the traversers 3, 4, 5 to the moving position of the industrial camera 1 based on the image data from the image processing device 11, exchanges data with the process control computer 15, etc. And performs overall control of the character reading device.

The operation procedure of the character reading apparatus in this embodiment will be described below with reference to the flow chart of FIG.

First, in step 1, each steel material 2 (3 types)
For each type of shape, the illuminance distribution when illuminating the end surface 2a at the same relative position as when reading characters is measured by an illuminometer or the like and stored in the image processing apparatus 11. Figure 3
This illuminance distribution is shown in (a). Here, the symbol A is the illuminance distribution of the steel material having the standard width and height in the present embodiment, and the symbol C is lower than that, that is, the distance of the printed characters to the lighting device 6 is short. , And the illuminance distribution of the steel material having a narrow width, and the reference character B is higher than the steel material of the reference character A, that is, the illuminance distribution of the steel material having a long print character distance with respect to the lighting device 6 and a narrow width. As is clear from this graph, the illuminance distribution pattern of the steel material end surface varies depending on the width and height of the steel material, that is, the shape.

In step 2, the end surface 2a of the steel material 2 is divided into a plurality of areas in the width direction for each type of the steel material 2, and a binarization threshold value is obtained for each area. Here, it is known that there is a certain correlation between the illuminance and the threshold value, and an example thereof is shown in FIG. From this relationship, the binarization threshold value of each region is obtained for each type of steel material 2, and the binarization threshold value is obtained.
Store in 1.

Then, in step 3, the steel material 2 is conveyed by the conveying device 7 while pressing the end surface 2a of the steel material 2 against the steel material end surface positioning mechanism 9 by a crane (not shown).
Then, the transportation is started in step 4, and the transportation is stopped when the front side edge of the steel material 2 in the transportation direction is detected by the position sensor 8 (step 5).

Next, in step 6, the illumination is turned on,
The camera 1 measures the width and height of the first end surface 2a of the steel material 2 to determine its type. And next step 7
The binarization threshold value is automatically set in accordance with the type of the steel material 2 photographed in, and the process proceeds to step 8.

In step 8, the character string 10 is actually cut out for each character, binarized with the above-mentioned binarization threshold value, each character is cut out, and a reference character pattern preset for each character and each cut out character The detected character is determined by comparing with the pattern, and the character string 10 is read. When the reading operation is completed, the steel material 2 is conveyed by the width of the read steel material and stopped (step 9).

Then, in step 10, it is judged whether or not the character reading of the steel material 2 of this set is completed. If not, the work of steps 6 to 9 is performed again,
If it is completed, the process returns to step 3 to read the characters of the next set of steel materials 2.

Needless to say, the present invention is not limited to the above-described embodiment and can be applied in various ways. For example, in this embodiment, as shown in step 1 and step 2 of the flow chart shown in FIG. The illuminance of each area was measured in advance for each type of steel material and the binarization threshold value was set and stored, but the illuminance distribution was measured each time before reading each steel material and the binarization threshold value was set for each steel material. It may be corrected or the stored binarization threshold may be corrected.

[0021]

As described above in detail, according to the character reading method of the present invention, each character printed on the surface of a plurality of types of objects is photographed, and the image is binarized with a preset threshold value. In a character reading method that identifies characters by extracting them and then specifies the characters, the illuminance distribution in each area of the surface of the object when illuminated is measured for each type of object, and the measurement is performed. By setting a threshold value for each object and each area from the result and binarizing the captured image of each area of each object with the threshold value corresponding to the area, the printing surface is not uniformly illuminated. Also, since the binarization threshold value is optimized for each area of each object, proper binarization can be performed, and the correlation rate of the extracted character pattern with respect to the reference pattern can be maintained at a high state. , Read reliability is improved.

[Brief description of drawings]

FIG. 1 is a device configuration diagram illustrating an embodiment of a character reading device to which the present invention is applied.

FIG. 2 is a flowchart showing a main part of a character reading algorithm by a character reading method according to the present invention.

FIG. 3A is a graph showing the relationship between the shape of the steel material end surface and the illuminance distribution of each of the divided areas, and FIG. 3B is a graph showing the relationship between the illuminance of the steel material end surface and the binarization threshold value. Is.

[Explanation of symbols]

 1 Industrial Camera 2 Steel 2a End Face 3, 4, 5 Traverser 6 Illuminator 7 Conveyor 8 Position Sensor 9 Steel End Face Positioning Mechanism 10 Character String 11 Image Processor 13 Computer 14 Traverser Controller 15 Process Management Computer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tetsuo Nakamura 46-59 Nakahara, Tobata-ku, Kitakyushu City Nippon Steel Corporation Machinery & Plant Division

Claims (3)

[Claims] 1. A character printed on the surface of a plurality of types of objects having mutually different shapes is illuminated by an illuminating device and photographed, respectively, and the photographed image is binarized to extract a pattern of the character portion, which is used as a reference. In a character reading method for identifying a character by comparing with a pattern, the illuminance distribution in each region of the object surface when illuminated by the illumination device is measured for each type of the object, and It is characterized in that a binarization threshold value is set for each area of each object from the measurement result, and a captured image of each area of each object is binarized with a threshold value corresponding to the area. Character reading method. 2. The character reading method according to claim 1, wherein the distance of the object with respect to the illumination device and the photographing means is made constant during image photographing. 3. The character according to claim 1 or 2, wherein the object is made of steel, and the characters printed on the steel are printed by a paint spraying type printing device. How to read.